Monogenic disorders (monogenic traits) are disorders caused by variation in a single gene and are typically recognized by their striking familial inheritance patterns. Examples include sickle cell anemia, cystic fibrosis, Huntington disease, and Duchenne muscular dystrophy.

By contrast, complex disorders (complex traits) are those in which multiple genes play a role, often together with environmental factors. These include many complex disorders such as cardiovascular disease, asthma, diabetes, and cancer susceptibility.

This topic review discusses the inheritance patterns of monogenic traits, including classic Mendelian inheritance patterns as well as non-Mendelian patterns of inheritance such as mitochondrial inheritance and sex-linked expression, variable expressivity, variable penetrance, and other effects.

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